Re: Jo vs. Bo
Since Aikido's jo originates from a) spear techniques (most likely Hozoin-ryu as a core) and b) bayonet fighting (which contains a lot of spear-derived methodology), it is unrelated to Muso Shindo Ryu.
As others have posted, the jo is easily transportable, easier and cheaper to obtain than a bo, yari or juken, and takes up less practice space in the dojo.
A couple of weeks ago I did some kumijo with one of us using a bo. Certainly the jo vs. bo required an adjustment of maai, but the techniques could all be done.
Someday I hope to be able to afford a practice juken and yari, just to expand on my understanding of jo.